Another contributing factor in the puzzling overrepresentation of conservative columnists is that how "interesting" an opinion is largely depends on how much it diverges from yours. So a liberal op-ed editor may be quite hard on other liberals, who don't sound, to him, like they're saying anything new. Conversely, he could be quite easy on conservatives, because even their basic arguments are, to him, analytically fresh and innovative. This is also why you get a lot of "liberal" columnists who spend their time attacking liberal orthodoxes, because attacks on things you believe in, like Social Security, are also "interesting" insofar as they challenge your biases. It's worth remembering that Paul Krugman, peace be upon him, actually began his public intellectual life as a neoliberal economics commentator who spent a lot of time berating the left for clinging to outdated nostrums. He later became a hard-edged liberal commentator, but it's doubtful the New York Times would have hired him had he begun that way.
